Not a real problem, but could somebody explain why data transfer is so terribly slow:

I've an Arduino Ethernet card with 8GB SD card.This SD card contains a complete html code including several jpg's and png's files.It's all working fine: the webbrowser gives a request, arduino delivers the html page via the SD card, the webbrowser asks for the images (as put in the html file) and Arduino sent the files.But an image of approx. 150kB takes about 20 seconds to load, what's the bottleneck around here?(Arduino, Wiznet 5100, SD card, libraries..)

In all my simplicity I think: 8 MHz arduino, pick a byte from SD, sent it over the internet etc., 150kB shouldn't take 20 seconds?